Image processing apparatus, image processing method, and image processing program

ABSTRACT

In a console according to an embodiment, a control unit functions as a generation unit that generates a tomographic image from a plurality of projection images, which have been captured by a radiation detector at each of a plurality of imaging positions with different irradiation angles, with radiation sequentially emitted from each of the plurality of imaging positions, using a reconstruction process. In addition, the control unit functions as a derivation unit that derives the degree of enhancement as a parameter value used in a frequency enhancement process which is an example of image processing for a tomographic image, on the basis of the image analysis result of a projection image corresponding to an irradiation angle of 0 degrees. Furthermore, the control unit functions as a correction unit that corrects the parameter value according to image processing used in the reconstruction process and an image processing unit that performs the image processing on a tomographic image on the tomographic image using the corrected parameter value.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2017-187890 filed on Sep. 28, 2017. Theabove application is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image processing apparatus, an imageprocessing method, and an image processing program.

Related Art

As a radiography method, so-called tomosynthesis imaging has been knownwhich sequentially emits radiation from each of a plurality of imagingpositions with different irradiation angles and captures a plurality ofprojection images at each imaging position using a radiation detector.In tomosynthesis imaging, a tomographic image is generated from aplurality of captured projection images by a reconstruction process.

In general, predetermined image processing, such as a frequencyenhancement process or a gradation process, is performed on aradiographic image interpreted by a user, such as a technician, in orderto assist the user's interpretation. Therefore, the predetermined imageprocessing is also performed on a tomographic image. For example,JP2008-114064A and JP2013-144097A disclose a technique that performspredetermined image processing for a tomographic image using a parameterobtained on the basis of a projection image.

However, the tomographic image is an image affected by thereconstruction process unlike the projection image. Therefore, in a casein which the parameter obtained on the basis of the projection image isapplied to the tomographic image as in the technique disclosed inJP2008-114064A and JP2013-144097A, an image with desired image qualityis not obtained by the influence of the reconstruction process and theimage quality of the tomographic image is likely to deteriorate.

SUMMARY

The present disclosure has been made in view of the above-mentionedproblems and an object of the present disclosure is to provide an imageprocessing apparatus, an image processing method, and an imageprocessing program that can prevent the deterioration of the imagequality of a tomographic image.

In order to achieve the object, according to the present disclosure,there is provided an image processing apparatus comprising: a generationunit that generates a tomographic image from a plurality of projectionimages, which have been captured by a radiation detector at each of aplurality of imaging positions with different irradiation angles, withradiation sequentially emitted from each of the plurality of imagingpositions, using a reconstruction process; a derivation unit thatderives a parameter value used in predetermined image processing whichis performed on the tomographic image, on the basis of an image analysisresult of at least one of the plurality of projection images; acorrection unit that corrects the parameter value according to imageprocessing used in the reconstruction process; and an image processingunit that performs the predetermined image processing on the tomographicimage using the parameter value corrected by the correction unit.

In order to achieve the object, according to the present disclosure,there is provided an image processing apparatus comprising: a generationunit that generates a tomographic image from a plurality of projectionimages, which have been captured by a radiation detector at each of aplurality of imaging positions with different irradiation angles, withradiation sequentially emitted from each of the plurality of imagingpositions, using a reconstruction process; a derivation unit thatderives a parameter value used in predetermined image processing whichis performed on the tomographic image, on the basis of an image analysisresult after image processing used in the reconstruction process isperformed on at least one of the plurality of projection images; and animage processing unit that performs the predetermined image processingon the tomographic image using the parameter value.

In the image processing apparatus according to the present disclosure,the reconstruction process may be performed by a filtered backprojection method and the image processing used in the reconstructionprocess may be a filtering process in the filtered back projectionmethod.

In the image processing apparatus according to the present disclosure,the predetermined image processing may be at least one of a frequencyenhancement process or a gradation conversion process.

In the image processing apparatus according to the present disclosure,the derivation unit may derive a feature amount from a cumulativehistogram which is the image analysis result and may derive theparameter value on the basis of the derived feature amount.

In the image processing apparatus according to the present disclosure,the plurality of radiographic images may be of the breast as an objectand the feature amount may be an amount of mammary gland of the breast.

In the image processing apparatus according to the present disclosure,the plurality of radiographic images may be of the breast as an objectand the derivation unit may derive the parameter value on the basis of amammary gland region and a fat region of the breast in the projectionimage which is the image analysis result.

In the image processing apparatus according to the present disclosure,the plurality of radiographic images may be of the breast as an objectand the derivation unit may derive the parameter value on the basis of acontrast value of a local region corresponding to the mammary gland ofthe breast which is the image analysis result.

In the image processing apparatus according to the present disclosure,at least one of the plurality of projection images may be a projectionimage obtained in a case in which the incident angle of the radiationwith respect to the radiation detector is 0 degrees.

In order to achieve the object, according to the present disclosure,there is provided an image processing method comprising: generating atomographic image from a plurality of projection images, which have beencaptured by a radiation detector at each of a plurality of imagingpositions with different irradiation angles, with radiation sequentiallyemitted from each of the plurality of imaging positions, using areconstruction process; deriving a parameter value used in predeterminedimage processing which is performed on the tomographic image, on thebasis of an image analysis result of at least one of the plurality ofprojection images; correcting the parameter value according to imageprocessing used in the reconstruction process; and performing thepredetermined image processing on the tomographic image using thecorrected parameter value.

In order to achieve the object, according to the present disclosure,there is provided an image processing method comprising: generating atomographic image from a plurality of projection images, which have beencaptured by a radiation detector at each of a plurality of imagingpositions with different irradiation angles, with radiation sequentiallyemitted from each of the plurality of imaging positions, using areconstruction process; deriving a parameter value used in predeterminedimage processing which is performed on the tomographic image, on thebasis of an image analysis result after image processing used in thereconstruction process is performed on at least one of the plurality ofprojection images; and performing the predetermined image processing onthe tomographic image using the parameter value.

In order to achieve the object, according to the present disclosure,there is provided an image processing program that causes a computer toperform: generating a tomographic image from a plurality of projectionimages, which have been captured by a radiation detector at each of aplurality of imaging positions with different irradiation angles, withradiation sequentially emitted from each of the plurality of imagingpositions, using a reconstruction process; deriving a parameter valueused in predetermined image processing which is performed on thetomographic image, on the basis of an image analysis result of at leastone of the plurality of projection images; correcting the parametervalue according to image processing used in the reconstruction process;and performing the predetermined image processing on the tomographicimage using the corrected parameter value.

In order to achieve the object, according to the present disclosure,there is provided an image processing program that causes a computer toperform: generating a tomographic image from a plurality of projectionimages, which have been captured by a radiation detector at each of aplurality of imaging positions with different irradiation angles, withradiation sequentially emitted from each of the plurality of imagingpositions, using a reconstruction process; deriving a parameter valueused in predetermined image processing which is performed on thetomographic image, on the basis of an image analysis result after imageprocessing used in the reconstruction process is performed on at leastone of the plurality of projection images; and performing thepredetermined image processing on the tomographic image using theparameter value.

According to the present disclosure, it is possible to prevent thedeterioration of the image quality of a tomographic image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram illustrating an example of the overallconfiguration of a radiography system according to a first embodiment.

FIG. 2 is a block diagram illustrating an example of the configurationof a console and a mammography apparatus according to the firstembodiment.

FIG. 3 is a diagram illustrating tomosynthesis imaging performed by themammography apparatus according to the first embodiment.

FIG. 4 is a flowchart illustrating an example of the flow of imageprocessing in the console according to the first embodiment.

FIG. 5 is a flow diagram schematically illustrating the flow of imageprocessing in a case in which image processing for a tomographic imageaccording to the first embodiment is a frequency enhancement process.

FIG. 6 is a flow diagram schematically illustrating the flow of imageprocessing in a case in which the image processing for a tomographicimage according to the first embodiment is the frequency enhancementprocess and a gradation conversion process.

FIG. 7 is a flowchart illustrating an example of the flow of imageprocessing in a console according to a second embodiment.

FIG. 8 is a flow diagram schematically illustrating the flow of imageprocessing in a case in which image processing for a tomographic imageaccording to the second embodiment is a frequency enhancement process.

DETAILED DESCRIPTION

Hereinafter, embodiments of the invention will be described in detailwith reference to the drawings. The embodiments do not limit theinvention.

First Embodiment

In this embodiment, a radiography system that captures a radiographicimage of the breast of a subject which is an example of an object willbe described in detail.

First, an example of the overall configuration of the radiography systemaccording to this embodiment will be described. FIG. 1 is aconfiguration diagram illustrating an example of the overallconfiguration of a radiography system 1 according to this embodiment.

As illustrated in FIG. 1, the radiography system 1 according to thisembodiment includes a console 6 and a mammography apparatus 10. In theradiography system 1 according to this embodiment, a user, such as adoctor or a radiology technician, operates the mammography apparatus 10to capture the radiographic image of the breast of the subject on thebasis of a command (imaging order) input from an external system (forexample, a radiology information system (RIS)) through the console 6.

FIG. 2 is a block diagram illustrating an example of the configurationof the console 6 and the mammography apparatus 10 according to thisembodiment. Hereinafter, the console 6 and the mammography apparatus 10according to this embodiment will be described with reference to FIGS. 1and 2.

The mammography apparatus 10 according to this embodiment is anapparatus that irradiates the breast compressed by a compression plate20 with radiation R (for example, X-rays) and captures the radiographicimage of the breast. In addition, the mammography apparatus 10 may be anapparatus that captures an image of the breast of the subject in a state(seated state) in which the subject sits down on a chair (including awheelchair) as well as a state (standing state) in which the subjectstands up. The mammography apparatus 10 may be any apparatus that cancapture the radiographic image of at least the breast of the subject.

In addition, the mammography apparatus 10 according to this embodimenthas a function of performing so-called tomosynthesis imaging (which willbe described in detail below) and simple imaging.

A holding portion 18 of the mammography apparatus 10 supports an imagingtable 16 provided in an imaging unit 12 and a radiation source 29 in astate in which an imaging surface 24 and the radiation source 29provided in a radiation emitting unit 28 are separated by apredetermined distance.

A radiation detector 11 that detects the radiation R transmitted throughthe breast and the imaging surface 24 of the imaging table 16 isprovided in the imaging table 16. The mammography apparatus 10 generatesa radiographic image on the basis of the radiation R detected by theradiation detector 11. However, the type of radiation detector 11 is notparticularly limited. For example, the radiation detector 11 may be anindirect-conversion-type radiation detector that converts the radiationR into light and converts the converted light into charge or adirect-conversion-type radiation detector that directly converts theradiation R into charge. In this embodiment, image data indicating theradiographic image output from the radiation detector 11 of themammography apparatus 10 is transmitted to the console 6.

A shaft (not illustrated) is provided in the imaging unit 12 of themammography apparatus 10 such that the imaging unit 12 can be rotatedwith respect to a base portion 14. The shaft is fixed to a supportportion 22 and the shaft and the support portion 22 are integrallyrotated.

Gears (not illustrated) are provided in the shaft provided in theimaging unit 12 and the holding portion 18. The gears can switch betweenan engaged state and a disengaged state to switch an operation statebetween a state in which the holding portion 18 and the shaft areconnected and are integrally rotated and a state in which the shaft isseparated from the holding portion 18 and idles. In a case in whichtomosynthesis imaging is performed, the shaft is separated from theholding portion 18 and idles. Means for switching between thetransmission and non-transmission of the power of the shaft is notlimited to the gear and various mechanical elements may be used.

As illustrated in FIG. 2, the mammography apparatus 10 according to thisembodiment includes the radiation detector 11, the radiation emittingunit 28, a control unit 60, a storage unit 62, an interface (I/F) unit64, an operation panel 66, and a radiation source driving unit 68. Theradiation detector 11, the radiation source 29, the control unit 60, thestorage unit 62, the I/F unit 64, the operation panel 66, and theradiation source driving unit 68 are connected to each other through abus 69 such as a system bus or a control bus.

The control unit 60 according to this embodiment includes a centralprocessing unit (CPU) 60A, a read only memory (ROM) 60B, and a randomaccess memory (RAM) 60C. The CPU 60A controls the overall operation ofthe mammography apparatus 10 in response to a command from the console6. For example, various programs including an image processing program(which will be described below) executed by the CPU 60A are stored inthe ROM 60B in advance. The RAM 60C temporarily stores various kinds ofdata.

For example, the image data of the radiographic image captured by theradiation detector 11 and various kinds of information are stored in thestorage unit 62. Examples of the storage unit 62 include a hard diskdrive (HDD) and a solid state drive (SSD). The I/F unit 64 transmits andreceives various kinds of information to and from the console 6 using atleast one of wireless communication or wired communication. For example,the operation panel 66 is provided as a plurality of switches in theimaging table 16 of the mammography apparatus 10. In addition, theoperation panel 66 may be provided as a touch panel.

The radiation source driving unit 68 rotates the shaft (not illustrated)provided in the imaging unit 12 to continuously move the radiationsource 29 of the radiation emitting unit 28 such that the radiationsource 29 is moved to a plurality of imaging positions with differentirradiation angles in tomosynthesis imaging. In this embodiment, asillustrated in FIG. 3, the radiation source driving unit 68 moves theradiation source 29 to the imaging positions where the irradiationangles of the radiation emitting unit 28 are different from each otherand which are spaced a predetermined angle θ apart, that is, thepositions where the incident angles of the radiation R with respect tothe radiation detector 11 are different from each other.

As illustrated in FIG. 3, the incident angle means an angle α formedbetween a line CL normal to a detection surface of the radiationdetector 11 and a radiation axis RC. Here, it is assumed that thedetection surface of the radiation detector 11 is substantially parallelto the imaging surface 24. Hereinafter, as illustrated in FIG. 3, apredetermined range in which the incident angles (irradiation angles)are different from each other in tomosynthesis imaging is referred to asan “incident angle range”. An example of the incident angle range is arange of ±10 degrees or ±20 degrees with respect to the line CL normalto the detection surface of the radiation detector 11.

The console 6 according to this embodiment controls the mammographyapparatus 10, using, for example, an imaging order or various kinds ofinformation acquired from an external system, such as an RIS, through awireless communication local area network (LAN).

As illustrated in FIG. 2, the console 6 according to this embodimentincludes a control unit 70, a storage unit 72, an I/F unit 74, a displayunit 76, and an operation unit 80. The control unit 70, the storage unit72, the I/F unit 74, the display unit 76, and the operation unit 80 areconnected to each other through a bus 83 such as a system bus or acontrol bus.

The control unit 70 according to this embodiment controls the overalloperation of the console 6. The control unit 70 according to thisembodiment includes a CPU 70A, a ROM 70B, and a RAM 70C. The CPU 70Acontrols the overall operation of the mammography apparatus 10 inresponse to a command from the console 6. For example, various programsincluding an image processing program (which will be described below)executed by the CPU 70A are stored in the ROM 70B in advance. The RAM70C temporarily stores various kinds of data.

For example, the image data of the radiographic image captured by themammography apparatus 10 and various kinds of information are stored inthe storage unit 72. Examples of the storage unit 72 include an HDD andan SSD.

The I/F unit 74 transmits and receives various kinds of information toand from the mammography apparatus 10 or external systems, such as anRIS and a picture archiving and communication system (PACS), using atleast one of wireless communication or wired communication.

The display unit 76 displays, for example, information related toimaging and the captured radiographic image. The operation unit 80 isused by a user to input, for example, a command to capture aradiographic image and a command related to image processing on thecaptured radiographic image. For example, the operation unit 80 may havethe form of a keyboard or the form of a touch panel integrated with thedisplay unit 76.

Next, the operation of the console 6 in the radiography system 1according to this embodiment will be described. In general,predetermined image processing, such as a frequency enhancement processor a gradation process, is performed on the radiographic image to beinterpreted by the user in order to assist the interpretation. Theconsole 6 according to this embodiment performs the above-mentionedpredetermined image processing (hereinafter, referred to as “imageprocessing for a tomographic image”) for a tomographic image. Ingeneral, a frequency enhancement process corresponding to the amount ofmammary gland is performed on the radiographic image of the breast.Therefore, hereinafter, for example, a case in which the predeterminedimage processing is the frequency enhancement process will be described.

As the operation of the console 6, an operation in a case in which imageprocessing is performed on the radiographic image obtained bytomosynthesis imaging will be described below. Hereinafter, theradiographic images captured by the radiation detector 11 at a pluralityof imaging positions with different irradiation angles are referred toas projection images in tomosynthesis imaging. In addition, in a case inwhich a tomographic image reconstructed from the projection images andthe projection images are generically referred to without beingdistinguished from each other, they are simply referred to as“radiographic images”.

FIG. 4 is a flowchart illustrating an example of the flow of imageprocessing performed by the console 6 according to this embodiment. FIG.5 is a flow diagram schematically illustrating the flow of imageprocessing in a case in which the image processing for a tomographicimage is the frequency enhancement process.

For example, in a case in which the console 6 according to thisembodiment receives a command to display a tomographic image from theuser through the operation unit 80 of the console 6, the CPU 70A of thecontrol unit 70 executes the image processing program stored in the ROM70B to perform the image processing illustrated in FIG. 4.

As illustrated in FIGS. 4 and 5, in Step S100, the control unit 70acquires a series of projection images 100 obtained by one tomosynthesisimaging operation. The acquisition destination of the projection imagesis not particularly limited as long as it is a device storing a desiredprojection image and may be, for example, any one of the storage unit 72of the host apparatus, the mammography apparatus 10, and a PACS.

Then, in Step S102, the control unit 70 generates a tomographic image110 from the series of projection images 100 acquired in Step S100 usinga reconstruction process. For example, the control unit 70 according tothis embodiment performs a scattered ray removal process of removing ascattered ray component on each of the series of projection images 100.Then, the control unit 70 calculates the amount of movement of aninterest of object between the series of projection images 100 on thebasis of the incident angle of the radiation R at each imaging positionwhere each projection image has been captured and reconstructs thetomographic image 110 using a so-called filtered back projection method(FBP).

The slice thickness of the generated tomographic image 110 is any slicethickness and may be a predetermined thickness or may be designated bythe user. In addition, the number of tomographic images 110 to begenerated may be predetermined and the slice thickness corresponding tothe thickness of the breast compressed by the compression plate 20 andthe number of tomographic images 110 to be generated may be used.

Then, in Step S104, the control unit 70 performs image analysiscorresponding to the image processing for a tomographic image on apredetermined projection image among the series of projection images100. For example, in this embodiment, the predetermined projection imageis a projection image 100B corresponding to an incident angle of 0degrees.

In this embodiment, as described above, the image processing for atomographic image is the frequency enhancement process. In the frequencyenhancement process, the degree of enhancement is used as a parametervalue. The degree of enhancement is determined on the basis of acumulative histogram of the pixel values of the radiographic image.Here, the control unit 70 derives the cumulative histogram of the pixelvalues of the projection image 100B using image analysis.

Then, in Step S106, the control unit 70 derives a parameter value 122Aof the image processing for a tomographic image. In this embodiment, thedegree of enhancement is derived as the parameter value 122A.

It has been known that, in a case in which the amount of mammary glandis different, the frequency of low-concentration data increases as theamount of mammary gland increases in pixel data of the radiographicimage. In a case in which the frequency of the histogram of the pixelvalues are cumulatively added from the low-concentration side and theamount of mammary gland is large, that is, the frequency oflow-concentration data is high, a cumulative value increases rapidly. Incontrast, in a case in which the amount of mammary gland is small, thecumulative value increases gradually. Therefore, the amount of mammarygland can be determined to be large in a case in which a signal valuewith a predetermined cumulative frequency (x %) is close to thelow-concentration side and can be determined to be small in a case inwhich the signal value is close to the high-concentration side.

For this reason, the control unit 70 analyzes the cumulative histogramof the image data of the projection image and derives a signal valuewith a predetermined cumulative frequency (x %) as a feature amountindicating a difference in the shape of the cumulative histogramdepending on the amount of mammary gland. For example, the control unit70 compares the derived signal with reference values that have beenpredetermined so as to correspond to three mammary gland amountcategories, that is, large, medium, and small categories, and classifiesthe signal value into three categories, that is, small, medium, andlarge categories. Then, the control unit 70 selects the degree ofenhancement of the frequency enhancement process corresponding to theclassification results of the signal value from high, medium, and lowlevels and derives the degree of enhancement.

Then, in Step S108, the control unit 70 corrects the parameter value122A derived in Step S106 according to image processing (hereinafter,referred to as “image processing corresponding to reconstruction”)corresponding to the reconstruction process used to generate thetomographic image in Step S102. In this embodiment, the reconstructionprocess is performed using the FBP method as described above. Therefore,the control unit 70 corrects the parameter value 122A according to afilter coefficient 120 of a filter used in the FBP method.

Then, in Step S110, the control unit 70 performs the image processingfor a tomographic image on the tomographic image 110 generated in StepS102 using the corrected parameter value 122B. In this embodiment, thecontrol unit 70 performs the frequency enhancement process on thetomographic image 110 using the corrected parameter value 122B as thedegree of enhancement.

Then, in Step S112, the control unit 70 displays the tomographic image110 subjected to the image processing for a tomographic image on thedisplay unit 76 and ends the image processing. The tomographic imagethat has been subjected to the frequency enhancement process accordingto a difference in the amount of mammary gland is displayed on thedisplay unit 76 by the image processing.

As such, in the console 6 according to this embodiment, the control unit70 functions as a generation unit that generates the tomographic image110 from a plurality of projection images 100A, which have been capturedby the radiation detector 11 at each of a plurality of imaging positionswith different irradiation angles, with the radiation R sequentiallyemitted the plurality of imaging positions, using the reconstructionprocess. In addition, the control unit 70 functions as a derivation unitthat derives the degree of enhancement as the parameter value used inthe frequency enhancement process which is an example of the imageprocessing for a tomographic image, on the basis of the image analysisresult of the projection image 100B corresponding to an irradiationangle of 0 degrees. Furthermore, the control unit 70 functions as acorrection unit that corrects the parameter value according to the imageprocessing used in the reconstruction process and an image processingunit that performs the image processing for a tomographic image on thetomographic image using the corrected parameter value.

In general, in tomosynthesis imaging, the irradiation angle of radiationis limited. Therefore, for example, in a case in which the projectionimages are superimposed by the FBP method using the reconstructionprocess to reconstruct the tomographic image, an artifact which is avirtual image of a structure is likely to be included in a region inwhich no structures are originally present in the object. Specifically,in some cases, back projection causes an artifact to be included in aregion in which no structures are originally present in a tomographicimage of a tomographic plane different from the tomographic image of thetomographic plane in which a structure is present. This phenomenonoccurs due to other reconstruction processing methods in addition to theFBP method.

Therefore, in a case in which image analysis is performed on thetomographic image in order to perform predetermined image processingsuch as a frequency enhancement process, it is difficult to obtainaccurate analysis results.

For this reason, the control unit 70 of the console 6 according to thisembodiment performs image analysis on the projection image and derivesthe parameter value of the image processing for a tomographic image onthe basis of the image analysis results.

Here, in the image processing for a tomographic image performed on thetomographic image, in a case in which the parameter value derived fromthe projection image is used without any change, the tomographic imageis affected by image processing, such as a filtering process, used inthe reconstruction process for generating a tomographic image from aprojection image. Therefore, in some cases, the image processing for atomographic image is not appropriately performed.

In contrast, the control unit 70 of the console 6 according to thisembodiment corrects the parameter value according to image processingused in the reconstruction process and performs the image processing fora tomographic image on the tomographic image 110 using the correctedparameter value.

Therefore, according to the console 6 of this embodiment, it is possibleto prevent the deterioration of the image quality of the tomographicimage 110.

In this embodiment, the aspect in which the image processing for atomographic image is a frequency enhancement process and the parametervalue is the degree of enhancement derived from the cumulative histogramderived by performing image analysis on the projection image 100B hasbeen described. However, the image processing for a tomographic image isnot particularly limited.

For example, in general, the mammographic image in which the amount ofmammary gland is large has a lower contrast and is more likely to be ablurred image than the mammographic image in which the amount of mammarygland is small. Therefore, a technique has been known which performs afrequency enhancement process and a gradation conversion process as theimage processing for a tomographic image on the basis of a contrastvalue in order to easily distinguish the mammary gland tissues from thefat tissues. As such, in a case in which the frequency enhancementprocess and the gradation conversion process are performed as the imageprocessing for a tomographic image, as illustrated in FIG. 6, in StepS104, the control unit 70 performs image analysis on the projectionimage 100B to detect a local region corresponding to the mammary glandin the mammographic image as a mammary gland region (low-concentrationregion) and derives the contrast values of the detected mammary glandregion and a fat region (high-concentration region). Then, the controlunit 70 obtains the contrast value as the parameter value 122A in StepS106 and corrects the parameter value 122A using the filter coefficient120 in Step S108. In Step S110, the control unit 70 performs the imageprocessing for a tomographic image using the corrected parameter value122B, adjusts the contrast of the mammary gland region(low-concentration region) using the gradation conversion process, andenhances the contrast of the fat region (high-concentration region)using the frequency enhancement process.

Second Embodiment

Next, a second embodiment will be described in detail. In thisembodiment, the same configuration and operation as those described inthe first embodiment are denoted by the same reference numerals and thedetailed description thereof will not be repeated.

Since the configuration of the radiography system 1 and theconfiguration of the console 6 and the mammography apparatus 10 are thesame as those in the first embodiment, the description thereof will notbe repeated. In this embodiment, image processing performed by thecontrol unit 70 of the mammography apparatus 10 is different from theimage processing (see FIG. 4) according to the first embodiment in someprocesses. Therefore, different processes will be described.

FIG. 7 is a flowchart illustrating an example of the flow of imageprocessing in the console 6 according to this embodiment. FIG. 8 is aflow diagram schematically illustrating the flow of image processing ina case in which the image processing for a tomographic image is afrequency enhancement process.

The image processing illustrated in FIG. 7 differs from the imageprocessing (see FIG. 4) according to the first embodiment in that aprocess from Step S105 to Step S111 is performed instead of the processfrom Step S104 to Step S110. Therefore, different processes will bedescribed.

In Step S105, the control unit 70 performs image processingcorresponding to reconstruction on the tomographic image 110 obtained byperforming the process in Step S102 on a predetermined projection imageamong a series of projection images 100. For example, in thisembodiment, the predetermined projection image is the projection image100B corresponding to an incident angle of 0 degrees as in the firstembodiment. The image processing corresponding to reconstructionaccording to this embodiment is image processing corresponding to afilter coefficient used in the reconstruction process.

Then, in Step S107, the control unit 70 performs image analysis on theprojection image 100B subjected to the image processing corresponding toreconstruction in Step S105 as in Step S104 (see FIG. 4) of the imageprocessing according to the first embodiment.

Then, in Step S109, the control unit 70 derives the degree ofenhancement as the parameter value 122C of the image processing for atomographic image as in Step S106 (see FIG. 4) of the image processingaccording to the first embodiment.

Then, in Step S111, the control unit 70 performs the image processingfor a tomographic image on the tomographic image 110 using the parametervalue 122B derived in Step S109 as in Step S110 of the image processingaccording to the first embodiment.

As described above, in this embodiment, the frequency enhancementprocess is performed on the tomographic image 110 using the correctedparameter value 122B which is the degree of enhancement.

As such, in the console 6 according to this embodiment, the control unit70 functions as a generation unit that generates the tomographic image110 from a plurality of projection images 100A, which have been capturedby the radiation detector 11 at each of a plurality of imaging positionswith different irradiation angles, with the radiation R sequentiallyemitted from each of the plurality of imaging positions, using thereconstruction process. In addition, the control unit 70 functions as aderivation unit that derives the degree of enhancement as the parametervalue 122C used in the frequency enhancement process which is an exampleof the image processing for a tomographic image, on the basis of theimage analysis result after image processing corresponding to thefiltering process used in the reconstruction process is performed on theprojection image 100B corresponding to an irradiation angle of 0degrees. Furthermore, the control unit 70 functions as an imageprocessing unit that performs the image processing for a tomographicimage on the tomographic image 110 using the parameter value 122C.

As described in the first embodiment, an artifact is generated in thetomographic image. Therefore, in a case in which image analysis isperformed on the tomographic image in order to perform predeterminedimage processing such as a frequency enhancement process, accurateanalysis results may not be obtained.

For this reason, the control unit 70 of the console 6 according to thisembodiment performs image processing corresponding to the filteringprocess used in the reconstruction process on the projection image,performs image analysis, and derives the parameter value of the imageprocessing for a tomographic image on the basis of the image analysisresult. Therefore, it is possible to derive the parameter valueconsidering the reconstruction process in the generation of atomographic image.

Therefore, according to the console 6 of this embodiment, it is possibleto prevent the deterioration of the image quality of the tomographicimage 110.

In each of the above-described embodiments, the case in which the FBPmethod is used as the reconstruction processing method for generating atomographic image has been described. However, the reconstructionprocessing method is not limited to the FBP method. As thereconstruction processing method, known reconstruction processingmethods, such as an algebraic reconstruction method, and successiveapproximation reconstruction method, may be used in addition to acomputed tomography (CT) reconstruction processing method such as ashift-and-add method. In a case in which any reconstruction processingmethod is used, image processing required for the reconstruction processis performed. Therefore, this image processing may be performed as theimage processing corresponding to reconstruction.

In each of the above-described embodiments, the aspect in which imageanalysis is performed on the projection image 100B corresponding to anincident angle of 0 degrees among a series of projection images 100obtained by tomosynthesis imaging and the parameter value is derived hasbeen described. However, the projection image used to derive theparameter value is not limited thereto. For example, a representativevalue (for example, an average value) of the parameter values obtainedby performing image analysis on a plurality of projection images 100 maybe derived. In this case, the plurality of projection images 100 may be,for example, all of the series of projection images 100B or may be theprojection images captured at the imaging positions at the center (anincident angle of 0 degrees) and both ends of the incident angle range.

In each of the above-described embodiments, the aspect in which theobject is the breast has been described. However, the object is notlimited to the breast and may be other parts such as the lung. Forexample, in a case in which the object is the lung and a frequencyenhancement process is performed as the image processing for atomographic image on a tomographic image for diagnosing a lung cancer inorder to make a lung field clear, the technique according to the presentdisclosure may be applied. In addition, in a case in which the imageprocessing for a tomographic image is performed in order to easilydistinguish bone tissues from soft tissues, the technique according tothe present disclosure may be applied.

In each of the above-described embodiments, various processors otherthan the CPU may perform the image processing performed by the executionof software (program) by the CPU. In this case, examples of theprocessor include a programmable logic device (PLD) whose circuitconfiguration can be changed after manufacture, such as afield-programmable gate array (FPGA), and a dedicated electric circuit,such as an application specific integrated circuit (ASIC), which is aprocessor having a dedicated circuit configuration designed to perform aspecific process. In addition, the image processing may be performed byone of the various processors or may be performed by a combination oftwo or more processors of the same type or different types (for example,a combination of a plurality of FPGAs and a combination of a CPU and anFPGA). Specifically, the hardware structure of the various processors isan electric circuit obtained by combining circuit elements such assemiconductor elements.

In each of the above-described embodiments, the aspect in which variousprograms stored in the control unit 60 of the mammography apparatus 10and the control unit 70 of the console 6 are stored (installed) in theROMs (60B and 70B) of the control unit 60 and the control unit 70 inadvance has been described. However, the invention is not limitedthereto. The image processing program may be recorded on a recordingmedium, such as a compact disk read only memory (CD-ROM), a digitalversatile disk read only memory (DVD-ROM), or a universal serial bus(USB) memory, and then provided. In addition, the image processingprogram may be downloaded from an external apparatus through thenetwork.

In each of the above-described embodiments, the radiation is notparticularly limited. For example, X-rays or y-rays may be applied.

In addition, for example, the configuration and operation of theradiography system 1, the console 6, and the mammography apparatus 10according to each of the above-described embodiments are illustrativeand may be changed according to the situation, without departing fromthe scope and spirit of the invention. In addition, the above-describedembodiments may be appropriately combined with each other.

What is claimed is:
 1. An image processing apparatus comprising: atleast one processor configured to: generate a tomographic image from aplurality of projection images, which have been captured by a radiationdetector at each of a plurality of imaging positions with differentirradiation angles, with radiation sequentially emitted from each of theplurality of imaging positions, using a reconstruction process; derive aparameter value used in predetermined image processing which isperformed on the tomographic image, on the basis of an image analysisresult of at least one of the plurality of projection images; correctthe parameter value according to image processing used in thereconstruction process; and perform the predetermined image processingon the tomographic image using the parameter value corrected by thecorrection unit.
 2. The image processing apparatus according to claim 1,wherein the reconstruction process is performed by a filtered backprojection method, and the image processing used in the reconstructionprocess is a filtering process in the filtered back projection method.3. The image processing apparatus according to claim 1, wherein thepredetermined image processing is at least one of a frequencyenhancement process or a gradation conversion process.
 4. The imageprocessing apparatus according to claim 1, wherein the at least oneprocessor is configured to derive a feature amount from a cumulativehistogram which is the image analysis result and to derive the parametervalue on the basis of the derived feature amount.
 5. The imageprocessing apparatus according to claim 4, wherein the plurality ofradiographic images are of the breast as an object, and the featureamount is an amount of mammary gland of the breast.
 6. The imageprocessing apparatus according to claim 1, wherein the plurality ofradiographic images are of the breast as an object, and the at least oneprocessor is configured to derive the parameter value on the basis of amammary gland region and a fat region of the breast in the projectionimage which is the image analysis result.
 7. The image processingapparatus according to claim 1, wherein the plurality of radiographicimages are of the breast as an object, and the at least one processor isconfigured to derive the parameter value on the basis of a contrastvalue of a local region corresponding to the mammary gland of the breastwhich is the image analysis result.
 8. The image processing apparatusaccording to claim 1, wherein at least one of the plurality ofprojection images is a projection image obtained in a case in which theincident angle of the radiation with respect to the radiation detectoris 0 degrees.
 9. An image processing method comprising: generating atomographic image from a plurality of projection images, which have beencaptured by a radiation detector at each of a plurality of imagingpositions with different irradiation angles, with radiation sequentiallyemitted from each of the plurality of imaging positions, using areconstruction process; deriving a parameter value used in predeterminedimage processing which is performed on the tomographic image, on thebasis of an image analysis result of at least one of the plurality ofprojection images; correcting the parameter value according to imageprocessing used in the reconstruction process; and performing thepredetermined image processing on the tomographic image using thecorrected parameter value.
 10. A non-transitory computer-readablestorage medium that stores an image processing program that causes acomputer to perform: generating a tomographic image from a plurality ofprojection images, which have been captured by a radiation detector ateach of a plurality of imaging positions with different irradiationangles, with radiation sequentially emitted from each of the pluralityof imaging positions, using a reconstruction process; deriving aparameter value used in predetermined image processing which isperformed on the tomographic image, on the basis of an image analysisresult of at least one of the plurality of projection images; correctingthe parameter value according to image processing used in thereconstruction process; and performing the predetermined imageprocessing on the tomographic image using the corrected parameter value.